1. Field of the Invention
The present invention relates to a semiconductor processing apparatus for processing a substrate, such as a semiconductor wafer or an LCD substrate, by heating the substrate in a process gas atmosphere.
2. Description of the Related Art
A CVD (Chemical Vapor Deposition) apparatus is known as an apparatus for processing a semiconductor wafer, such as a silicon wafer, or a glass substrate for LCD. In the CVD apparatus, it is important to equally heat an entire surface of the wafer at a predetermined temperature so as to uniformly form a thin film on the wafer.
FIG. 6 shows a conventional CVD apparatus using a resistance heater. In this apparatus, a work table 2 is provided to be supported by a support 4 in a lower portion of a process space defined by a vacuum process chamber 1. The work table 2 comprises a resistance heating body 2a and electrical insulating plates 2b, 2b superimposed on both sides of the heating body 2a. A graphite plate 3, which forms a wafer mounting surface, is layered on the surface of the upper insulating plate 2b. A feeder 5 is connected to the resistance heating body 2a. The feeder 5 is surrounded by a sheath wire (not shown), and drawn to the outside of the process chamber 1. A sheath thermocouple 6, which stores a thermocouple in the sheath wire, contacts the resistance heating body 2a.
In such a film forming apparatus, the inside of the process chamber 1 is exhausted to obtain a predetermined degree of vacuum. Then, a process gas is supplied thereto from a gas supply section 8 in a state that the predetermined degree of vacuum is maintained. Moreover, electric power is supplied to the resistance heating body 2a through the feeder 5, and a temperature of a wafer W is controlled to be a predetermined temperature based on a temperature detecting value of the sheath thermocouple 6.
As a resistance heater, there is known a ceramic heater wherein a resistance heating wire is buried in a ceramic plate and a wafer is mounted on the ceramic plate.
In the CVD apparatus, there is a case in which a corrosive gas is used as a process gas or a corrosive gas is generated by reaction of a process gas. For example, in a case that a halide gas is used, a halogen gas having strong corrosiveness is generated by vapor phase reaction. Moreover, since the temperature is increased during a process, corrosiveness of the halogen gas is extremely strong. Due to this, the feeder 5, the resistance heating body 2a, and their terminals, which are exposed in the process gas atmosphere, are corroded.
When the circuit elements are corroded, the resistance value of the resistance heater is increased. As a result, a current supplied to the heater is deviated from a predetermined value, and breaking of wire occurs. Beside the corrosion problem, in forming a conductive film, e.g., a metallic film on the wafer, the metallic film is adhered to the portion between the terminals of the feeder 5 and a short circuit is caused. This can also prevent the electric power from being stably supplied to the resistance heater. Due to this, the temperature of wafer W becomes unstable, and the thickness and the property of a formed film are less uniform over the entire surface of the wafer W.
Also, there are problems in the thermocouple as follows.
More specifically, the thermocouple is exposed in the process chamber 1, and the response changes depending on the degree of vacuum. For example, when pressure is largely changed by the supply of a process gas, the temperature is overshot, and the detection of the temperature is not correctly performed. Due to this, when forming the film, the heater temperature and the wafer temperature become unstable, and the stable film forming process cannot be performed.
If the ceramic heater is used, the above disadvantage can be relaxed, since the resistance heating wire is not directly exposed in the process gas atmosphere. However, if the sheath wire and the ceramic plate are directly bonded, a crack is generated in the ceramic by the difference in the coefficient of thermal expansion. Due to this, the terminals of the resistance heating wire cannot help being exposed. Therefore, there occurs a problem of corrosion therein.
Moreover, the ceramic heater has an extremely large heat capacity, and can be neither rapidly heated nor cooled. Due to this, it is needed that the ceramic heater be maintained in an ON state during wafer exchange when a plurality of wafers are processed. However, if the wafer W is mounted on the ceramic heater, which is maintained in a heating state, the wafer is rapidly heated from the room temperature, and subjected to heating damage. Moreover, there is a problem in that a transfer arm for dealing with the wafer is deformed by heat.